Agricultural chemical formulations in a solid state which contain agricultural chemical active ingredients are used as a spray into water such as in rice paddy fields. If an agricultural chemical active ingredient exhibits high water solubility, the agricultural chemical active ingredient may be released too quickly from the agricultural chemical formulation. If the release speed of the agricultural chemical active ingredient is too high, problems may arise in that phytotoxicity may occur, and a sufficient residual effect may become unobtainable.
In order to solve these problems, so far, agricultural chemical formulations from which the release of the agricultural chemical active ingredient is controlled, have been proposed and developed. For example, Patent Document 1 proposes an agricultural chemical-containing resin composition obtained by mixing: (a) at least one type of readily water-soluble agricultural chemical raw material; (b) a water-insoluble substance or a poorly water-soluble substance having a melting point or a softening point of 50° C. or higher but lower than 130° C.; and (c) white carbon, under heating at the melting point or the softening point of the substance (b) or a higher temperature but below 130° C.
Moreover, Patent Document 2 proposes: a release-controlled agricultural chemical formulation for water surface application having an excellent property to float and disperse, which comprises an agricultural chemical-containing resin composition comprising an agricultural chemical active ingredient, polyethylene, and hydrophobic silica; a production method thereof; and a release-controlled agricultural chemical composition.
However, even with such an agricultural chemical composition or an agricultural chemical formulation as described in Patent Documents 1 and 2, the control of the release of the agricultural chemical active ingredient is not always sufficient. Thus, there has been a demand for the development of agricultural chemical compositions from which the release of the agricultural chemical active ingredient is sufficiently controlled.
In addition, Patent Document 3 proposes an agricultural chemical formulation wherein a composition comprising an agricultural chemical active ingredient, a styrene-maleic anhydride copolymer, and a release-controlling agent (a water soluble polymer, silicon oxide, or a surfactant), is in a compatible state or forms a matrix. Furthermore, Patent Document 4 proposes an agricultural chemical formulation wherein a composition comprising an agricultural chemical active ingredient, a styrene-maleic anhydride copolymer, and a metal salt of a fatty acid as a release-controlling agent, is in a compatible state or forms a matrix. In Patent Documents 3 and 4, a composition using 50% by mass of hydrophilic white carbon is described as a comparative example. The composition exhibits a high initial burst (the release rate after 15 minutes from the addition to water), and after 72 hours falls to a state, being so-called dead stock, in which the release rate stops increasing.